Based on AP75x2 family design there is an antenna diplexer used.
This brings necessary attenuation for Tx radio power as this does not count with antenna gain, but takes in consideration all loss.
As can be found in data sheet for AP7522 / AP7532
Internal Antennas (AP-75x2-67030-xx)
2.4 GHz Band : max 23 dBm / 4 dBi antenna gain
5 GHz Band : max 23 dBm / 6 dBi antenna gain
The maximum possible radio power could be then seen below.
I manually set too high
value - in brackets - and system automatically attenuates
Tx power to comply with regulations.
Observe also maximum power allowed by regulatory for a group of channels.
The math is done as follows:
maximum allowed power + diplexor attenuation + MIMO subtraction (when used) + antenna gain = Tx power
Diplexer halves the antenna gain so using numbers it shall look like this
R1 (no MIMO): 20 dBm = 18 dBm - ~2 dBi + 4 dBi
R2 (no MIMO): 23 dBm = 20 dBm - ~3 dBi + 6 dBi
When MIMO is actually in place it shall be also seen in Tx power. MIMO subtraction goes up to 2 dBi as far as I remember
R1 (MIMO): 20 dBm = 20 dBm - ~2 dBi - 2 dBi + 4 dBi
R2 (MIMO): 23 dBm = 22 dBm - ~3 dBi - 2 dBi + 6 dBi